Enhanced erodibility of deep-sea sediments by presence of calcium carbonate particles
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ORIGINAL
Enhanced erodibility of deep-sea sediments by presence of calcium carbonate particles Jun Young Seo 1 & Sun Min Choi 1 & Ho Kyung Ha 1 & Kyung Eun Lee 2 Received: 8 October 2019 / Accepted: 13 March 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Using an erosion chamber, erodibility experiments on two different deep-sea sediments (mainly clayey silt) acquired in the western Pacific Ocean have been conducted to estimate the erosion rate and its potential controlling factors. Overall, the erosion rates of both deep-sea sediments were in the range of 10−7–10−5 kg m−2 s−1 which was two or three orders of magnitude lower than that of sediments in shallow environments. Such erodibility, however, exhibited two contrasting patterns depending on the carbonate compensation depth (CCD), which determines carbonate contents in sediments. At one site (MC1), above the CCD, the sediments (carbonate content 18.32 ± 1.00 wt%) were easily resuspended by surface erosion, resulting in a high eroded mass (2.49 × 10−2 kg m−2 at shear stress of 0.6 Pa). At another site (MC4), below the CCD, the sediments (carbonate content 0.06 ± 0.04 wt%) were less resuspended by floc erosion, resulting in a low eroded mass (3.70 × 10−3 kg m−2 at shear stress of 0.6 Pa). Over the entire range of bed shear stress, the erosion rate above the CCD was about 1–6 times higher than that below the CCD. The difference in carbonate content between two sites caused different variations in the bed resistance with depth. The erodibility above the CCD was enhanced, probably due to the particle roughness and low bulk density. Once the bed shear stress exceeded about 0.39 Pa, the erosion type of MC1 shifted from depth-limited to transitional erosion. However, the erosion type of MC4 always remained depth-limited over the entire range of bed shear stress. These results underline the effect of calcium carbonate on resuspension and erosion behaviors of the deep-sea sediments. Keywords Deep-sea sediment . Erodibility . Erosion rate . Critical shear stress . Carbonate compensation depth
Introduction Sediment erosion is determined by the balance between shear stress driven by external hydrodynamic forcings (e.g., tide, wave, current, and wind) and internal resistance of the sediment bed (Thomsen and Gust 2000; Mehta 2013; Ha et al. 2018). When the applied bed shear stress (τb) exceeds a critical value for erosion (τce), surface sediments start to move from their initial position, leading to sediment resuspension and erosion. Once the sediments are eroded, they are transported to the adjacent bed or into the
* Ho Kyung Ha [email protected]; [email protected] 1
Department of Ocean Sciences, Inha University, Incheon 22212, Republic of Korea
2
Department of Ocean Science, Korea Maritime and Ocean University, Busan 49112, Republic of Korea
overlying water column (Winterwerp and van Kesteren 2004; Ha and Maa 2009; Pilskaln et al. 2014). Sediment erodibility can be quantified as the amount of removed sediment exerted by erosion processes
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